As the density of data tracks on magnetic discs continues to increase, increased efficiency of the magnetic read/write head is required. Perpendicular recording, as opposed to the more conventional longitudinal recording, is a form of magnetic recording in which magnetic moments representing bits of data are orientated perpendicularly to the surface of the recording layer of the recording medium. Perpendicular recording may offer advantages over longitudinal recording, such as the ability to achieve higher linear densities, which may be important to extend disc drive technology beyond current data density limitations.
To further increase linear density, double layer media may be used in conjunction with perpendicular magnetic heads. Typically the double layer perpendicular media may consist of a high coercivity thin storage layer with perpendicular to-plane anisotropy and a soft magnetic underlayer (keeper) with in-plane anisotropy and relatively high permeability.
U.S. Pat. No. 5,181,151 ('151), issued to Masami Yamashita et al, describes a perpendicular recording head having a main pole and a return pole. The space between the main pole and return pole is the write gap. Magnetization transitions on the double layer perpendicular media are recorded by the trailing top edge of the main pole. The recorded transitions reproduce the shape of the main pole projected on the media. The write head of the '151 patent can not control the width of the recorded tracks and hence cannot be used effectively for high track density recording. Further, distribution of the write field across the track width formed by the head as described by Yamashita et al, has a “bell” like shape. The width of the recorded track is defined by the main pole width, write current, media coercivity and space between the head and the soft magnetic underlayer of the media. Due to the shallow field decay profile in cross-track direction, the recorded tracks of the device described in the '151 patent are relatively wide and there is a probability of adjacent track erasure. Thus, there is a need for a magnetic head having controllable width of recorded track and suppressed skew effect.
A recording head with controllable track width is described in U.S. Pat. No. 4,656,546. The magnetic head in patent '546 includes a main pole, a return pole, a write gap G between the main pole and return pole, and side shields on either side of the main pole that create side gaps Gs. Transitions are recorded at the trailing edge of the main pole that is adjacent to the write gap. The length of the write and side gaps are scaled by the distance D, which is the distance between the head air bearing surface (ABS) and the soft magnetic underlayer of the double layer media. As described in the '546 patent, the distance of write gap G is in the range from D/2 to 2D and the distance of side gaps Gs can be larger than the distance G. The distances of write gap and side gaps that is described in the '546 patent substantially reduce efficiency of the writer and do not support high-track density recording on high coercivity media. The write field in the media of the device described in the '546 patent is believed to barely exceed 6000 Oe and the writer cannot support recording on media with coercivity above 3000 Oe. Hence the head can only be used to record on perpendicular media with a coercivity up to 3000 Oe and a saturation field up to 6000 Oe. That limits the application of '546 high areal density recording due to necessity of higher media coercivity exhibiting high thermal stability. Thus there is a need for a magnetic head that can record on perpendicular media with a saturation field larger than 6000 Oe. The present invention addresses these and other needs and provides advantages that will become apparent to those skilled in the art.